Rollup merge of rust-lang#38664 - apasel422:may-dangle, r=pnkfelix

Replace uses of `#[unsafe_destructor_blind_to_params]` with `#[may_dangle]`

CC rust-lang#34761

r? @pnkfelix

Author: steveklabnik

src/liballoc/arc.rs

@@ -708,7 +708,7 @@ impl<T: ?Sized> Arc<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Drop for Arc<T> {
+unsafe impl<#[may_dangle] T: ?Sized> Drop for Arc<T> {
     /// Drops the `Arc`.
     ///
     /// This will decrement the strong reference count. If the strong reference
@@ -736,7 +736,6 @@ impl<T: ?Sized> Drop for Arc<T> {
     /// drop(foo);    // Doesn't print anything
     /// drop(foo2);   // Prints "dropped!"
     /// ```
-    #[unsafe_destructor_blind_to_params]
     #[inline]
     fn drop(&mut self) {
         // Because `fetch_sub` is already atomic, we do not need to synchronize

src/liballoc/lib.rs

@@ -79,9 +79,10 @@
 #![feature(const_fn)]
 #![feature(core_intrinsics)]
 #![feature(custom_attribute)]
-#![feature(dropck_parametricity)]
+#![feature(dropck_eyepatch)]
 #![cfg_attr(not(test), feature(exact_size_is_empty))]
 #![feature(fundamental)]
+#![feature(generic_param_attrs)]
 #![feature(lang_items)]
 #![feature(needs_allocator)]
 #![feature(optin_builtin_traits)]

src/liballoc/raw_vec.rs

@@ -539,8 +539,7 @@ impl<T> RawVec<T> {
     }
 }
 
-impl<T> Drop for RawVec<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for RawVec<T> {
     /// Frees the memory owned by the RawVec *without* trying to Drop its contents.
     fn drop(&mut self) {
         let elem_size = mem::size_of::<T>();

src/liballoc/rc.rs

@@ -644,7 +644,7 @@ impl<T: ?Sized> Deref for Rc<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T: ?Sized> Drop for Rc<T> {
+unsafe impl<#[may_dangle] T: ?Sized> Drop for Rc<T> {
     /// Drops the `Rc`.
     ///
     /// This will decrement the strong reference count. If the strong reference
@@ -672,7 +672,6 @@ impl<T: ?Sized> Drop for Rc<T> {
     /// drop(foo);    // Doesn't print anything
     /// drop(foo2);   // Prints "dropped!"
     /// ```
-    #[unsafe_destructor_blind_to_params]
     fn drop(&mut self) {
         unsafe {
             let ptr = *self.ptr;

src/libarena/lib.rs

@@ -30,10 +30,10 @@
 
 #![feature(alloc)]
 #![feature(core_intrinsics)]
+#![feature(dropck_eyepatch)]
 #![feature(heap_api)]
-#![feature(heap_api)]
+#![feature(generic_param_attrs)]
 #![feature(staged_api)]
-#![feature(dropck_parametricity)]
 #![cfg_attr(test, feature(test))]
 
 #![allow(deprecated)]
@@ -258,8 +258,7 @@ impl<T> TypedArena<T> {
     }
 }
 
-impl<T> Drop for TypedArena<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for TypedArena<T> {
     fn drop(&mut self) {
         unsafe {
             // Determine how much was filled.

src/libcollections/btree/map.rs

@@ -137,8 +137,7 @@ pub struct BTreeMap<K, V> {
 }
 
 #[stable(feature = "btree_drop", since = "1.7.0")]
-impl<K, V> Drop for BTreeMap<K, V> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] K, #[may_dangle] V> Drop for BTreeMap<K, V> {
     fn drop(&mut self) {
         unsafe {
             for _ in ptr::read(self).into_iter() {

src/libcollections/lib.rs

@@ -35,10 +35,11 @@
 #![feature(box_syntax)]
 #![cfg_attr(not(test), feature(char_escape_debug))]
 #![feature(core_intrinsics)]
-#![feature(dropck_parametricity)]
+#![feature(dropck_eyepatch)]
 #![feature(exact_size_is_empty)]
 #![feature(fmt_internals)]
 #![feature(fused)]
+#![feature(generic_param_attrs)]
 #![feature(heap_api)]
 #![feature(inclusive_range)]
 #![feature(lang_items)]

src/libcollections/linked_list.rs

@@ -726,8 +726,7 @@ impl<T> LinkedList<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for LinkedList<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for LinkedList<T> {
     fn drop(&mut self) {
         while let Some(_) = self.pop_front_node() {}
     }

src/libcollections/vec.rs

@@ -1763,8 +1763,7 @@ impl<T: Ord> Ord for Vec<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for Vec<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for Vec<T> {
     fn drop(&mut self) {
         unsafe {
             // use drop for [T]
@@ -2033,8 +2032,7 @@ impl<T: Clone> Clone for IntoIter<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for IntoIter<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for IntoIter<T> {
     fn drop(&mut self) {
         // destroy the remaining elements
         for _x in self.by_ref() {}

src/libcollections/vec_deque.rs

@@ -69,8 +69,7 @@ impl<T: Clone> Clone for VecDeque<T> {
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
-impl<T> Drop for VecDeque<T> {
-    #[unsafe_destructor_blind_to_params]
+unsafe impl<#[may_dangle] T> Drop for VecDeque<T> {
     fn drop(&mut self) {
         let (front, back) = self.as_mut_slices();
         unsafe {